friends/relatives listed on ship manifests

friends/relatives listed on ship manifests

On my grandfather's ship record, there is a person mentioned that was probably not a family member. His name was Rosenbaum, my grandfather was Katzman. He is listed as a cousin. I don't believe that he was. There are no Rosenbaums in that side of the family. Was this a common thing that happened, people listed as contacts that were called cousins and weren't? Did the authorities check these listings?